The invention relates to a disc brake for a commercial vehicle. The invention also relates to a brake pad set.
In the case of a generic disc brake, also known as a sliding-caliper brake, in a braking situation, an action-side brake pad is pressed against a vehicle-side brake disc by way of an application device, which is actuable pneumatically or by electric motor. During the further course of the braking process, the brake caliper is, relative to the brake disc, displaced counter to the application direction of the action-side brake pad, causing the opposite, reaction-side brake pad to be driven along and pressed against the other side of the brake disc.
In the case of the known disc brake, after a release of the brake, the brake caliper remains in said position, in which the brake pads, or at least the reaction-side brake pad, lies against the brake disc duly without pressure but with a rubbing action. The residual rubbing torques of the brake pads that thereby arise during driving operation have a disadvantageous effect because they lead to increased fuel consumption and to a reduction of the service life of the components involved, specifically of the brake disc and of the brake pads.
It is duly the case that the brake pads are released slightly during driving operation for example as a result of a wobbling movement of the brake disc and as a result of vibrations and lateral accelerations during cornering. These effects are however not sufficient to prevent said residual rubbing torques in an effective manner.
To counteract this problem, the generic DE 10 2007 001 213 discloses a disc brake having a resetting device which is arranged in one of the guide beams by way of which the brake caliper is displaceably held on the brake carrier, which resetting device has a resilient resetting element by means of which the brake caliper is displaced into an initial position.
This construction has proven successful in principle. However, the use of said known resetting device can lead to problems in the case of compressed-air-actuated disc brakes of heavy commercial vehicles, because here, there are wide-ranging influences resulting from component tolerances and component deformations, which have the effect that reliable functioning of said resetting device is not permitted in all situations.
Similar problems arise in the case of a disc brake such as that to which DE 10 2012 006 111 A1 relates. Here, a resetting device is arranged on the side which is situated opposite the application device and which faces toward the reaction-side brake pad, whereby effective, in particular automatic resetting of the brake caliper is realized, with a simultaneously minimal effect on the system rigidity
In any case, the resetting device acts on the brake caliper, wherein the brake carrier functions as a counterbearing.
DE 43 01 621 A1 describes a floating-caliper disc brake having a positionally static brake carrier which has two carrier arms which project over the outer edge of a brake disc, having brake shoes which are arranged on both sides of the brake disc and which have in each case one friction pad and one rear plate and which are supported displaceably on the carrier arms, having a floating caliper which is guided axially displaceably on the brake carrier and which engages around the brake shoes and has an actuating device designed for pressing the brake shoes against the brake disc, having a spring arrangement which acts axially on the brake shoes in a brake release direction and which, after the braking operation, assists in the setting of an air gap between the brake shoes and the brake disc. The spring arrangement has at least one spreading spring which is fastened in altogether non-displaceable fashion in an axial direction to a carrier arm of the brake carrier, in that the fastening is performed to a section of the carrier arm situated over the outer edge of the brake disc, and in that the spreading spring has at least two spring arms which lie resiliently in an axial direction against the rear plates of the brake shoes.
US2014/0339026 A1 describes a spreading spring comprising a locking arm which connects the spreading spring to a brake component, a retraction arm; and a preload device which is arranged between the locking arm and the retraction arm, wherein the preload device comprises six or more spiral-shaped loops which store energy during a braking activation and which retract the brake components (brake pad) as soon as the braking process has ended. A brake caliper in the form of a floating caliper, which is not a sliding caliper, is specified. This is suitable for a passenger vehicle but not for a commercial vehicle.
The invention is based on the object of further developing a disc brake of the generic type such that, with the simplest structural means, the service life in particular of the brake pads and of the brake disc is lengthened, and the operating costs are altogether lowered.
A further object consists in providing a corresponding brake pad set.
Said object is achieved by way of a disc brake according to embodiments of the invention.
The further object is achieved by way of a brake pad set according to embodiments of the invention.
A disc brake according to the invention for a commercial vehicle, having a brake caliper which engages over a brake disc and which is in the form of a sliding caliper and which is fastened to a positionally static brake carrier and which has a central opening over the brake disc, comprises two brake pads which are arranged in the brake caliper and which are movable in opposite directions and which have in each case one pad carrier plate and one friction pad fastened thereto and of which an action-side or application-side brake pad can be pressed against the brake disc by way of an application device via at least one brake plunger, and comprises at least one resetting device by means of which the brake caliper can be reset after a braking-induced displacement and release of the brake, wherein the resetting device has a spreading device which engages on the opposite brake pads and which acts equally counter to the respective application direction and which has resilient spreading elements which engage on the respective pad carrier plate. The spreading device is arranged in the central opening, wherein the spreading elements engage, outside the friction pads, directly or indirectly on at least two abutment regions arranged spaced apart from one another relative to the center, of the brake pads, wherein the spreading device has spring arms which, in the central region of the opening, are connected to one another and to a retaining bow which is attached to the brake carrier.
By means of the design of the disc brake according to the invention, synchronous resetting of both brake pads and resetting of the brake caliper when the brake is released are realized, wherein the synchronous resetting relates both to the resetting forces and to the resetting travels. Here, the resetting force acts counter to the respective application direction of the two brake pads, that is to say, in the case of the reaction-side brake pad, toward the caliper rear section, and in the case of the action-side brake pad, toward the caliper head, with gaps with respect to the brake disc being formed.
The spreading device expediently engages on the two brake pads at the pad carrier plates, specifically on the side facing toward the friction pad fastened thereto or on the opposite rear side. To prevent jamming of the respective brake pad during the resetting movement, the spreading element engages either centrally on an upper exposed edge region of the pad carrier plate or symmetrically on two abutment regions to the right and to the left.
The attachment of the retaining bow to the brake carrier permits retrofitting of the resetting device without modification to the brake caliper or to the brake carrier of the disc brake.
A brake pad set according to the invention for the disc brake according to the invention has at least two brake pads with in each case one pad carrier plate and with a friction pad attached to the pad carrier plate, and has the spreading device as indicated above. A retaining section of a pad carrier plate of a brake pad is produced on a thrust side of the pad carrier plate, in the manner of a stirrup, without undercuts with an opening and with a recess on a pad side of the pad carrier plate for a plate, in one piece with the pad carrier plate as a cast part. This is inexpensive, because no cores are required for the casting process, and no retroactive machining operations are necessary.
In one embodiment, the spreading elements extend, proceeding from a central region in the center of the opening, from the inside to the outside to the abutment regions which are arranged spaced apart from one another uniformly relative to the center. A compact construction is thus possible.
In this way, the spreading device is arranged in the center in the brake caliper, wherein said spreading device is likewise arranged within an envelope of a wheel rim of an associated wheel.
The two spreading elements are connected to one another in the center (in relation to the carrier horns). It is thus possible to ensure a spring force which is identical—in a small tolerance range—both on the run-in side and on the run-out side. Different spring forces between run-out side and run-in side, which can lead to oblique wear, are minimized by way of the unilateral engagement of in each case one spring per pad.
A further embodiment provides that the central region of the opening extends to both sides of a virtual center of the opening approximately parallel to the plane of the brake disc over a length in a range from 30 to 50% of a longitudinal axis of the opening. This yields an advantageous adaptation of the spring forces.
In another embodiment, the spreading device has spring arms, of which in each case two lie against an associated pad carrier plate, wherein the spring arms are connected to one another in the central region of the opening, which simplifies installation during assembly and maintenance work.
According to a further concept of the invention, the spreading device has oppositely acting spreading elements, preferably with elastic action, in particular in the form of spring elements.
According to one concept of the invention, the spreading device is operatively connected to the brake carrier, which forms a counterbearing and in which the brake pads are mounted so as to be displaceable coaxially with respect to the brake disc.
For this purpose, the retaining bow is preferably provided, which extends across the brake disc in the circumferential region as far as brake carrier horns, which delimit a pad slot at both sides, of the brake carrier. The retaining bow is not a pad retaining stirrup, but is an additional component.
In one embodiment, the retaining bow may be attached to two mutually oppositely situated stirrups which are connected to the brake carrier, which permits simple attachment.
Alternatively, the retaining bow may be arranged in the region of an application-side edge of the opening, whereas the spreading elements, which engage on the two brake pads, are connected to the retaining bow. Said retaining bow thus forms a centering device which, in correspondence with the brake carrier as a fixed bearing, may also be realized in some other way in terms of construction.
The retaining bow is preferably attached in a positionally static manner between the brake carrier and bearing beams of the brake caliper. For this purpose, the retaining bow may have at least one fastening section with an opening which is arranged coaxially with respect to a bearing receptacle of the brake carrier, to which the brake caliper is fastened by means of a bearing beam. This yields the advantage that, for the attachment of the retaining bow, no modifications need to be made to the brake caliper or to the brake carrier.
By way of the retaining bow to which, in one embodiment, the spreading device is fastened by way of its spring arms by means of a retaining stirrup, automatic centering of the brake caliper after a release of the brake, that is to say after the ending of a braking process, is realized, wherein, by way of the thus fixed positioning of the spreading device, the brake pads are reset such that the brake caliper is centered relative to the brake disc.
For this purpose, the spring arms are connected by means of a retaining stirrup to the retaining bow, wherein the retaining stirrup has two retaining arms, each of which extends beyond the retaining bow and is fixedly connected to the latter. A simple and stable construction can be realized in this way.
Furthermore, the spreading device is designed so as to act over the entire range of wear of the brake pads.
Since the points of force engagement on the brake pads change with progressive wear, those functional parts of the spreading device which make contact with the brake pads are designed so as to be supported in sliding fashion on the pad carrier plate of the respective brake pads.
To ensure secure retention of the spring limbs, or, in the case of a different design variant, of the spring arms, even under the action of vibrations during driving operation, the spring arms are supported on the upper edge of the pad carrier plate in relation to the base of the pad slot, likewise in sliding fashion as described above.
The structural realization of the spreading device according to the invention may differ in terms of construction, wherein a major advantage emerges from the fact that it is possible to substantially dispense with moving components, self-evidently with the exception of the resilient spreading elements which, for their function, perform a resilient deflection.
The omission of moving parts that is now possible self-evidently has the effect of lengthening the service life of the spreading device, as does the low number of components required, resulting, moreover, in extremely inexpensive production and assembly.
In a further embodiment, the spring arms may be formed as two pairs of spring arms, wherein the pairs are arranged opposite one another in a longitudinal direction of the opening such that they are fastened by way of inner ends, which are in each case connected by means of a connecting section, in the center of the opening to the retaining stirrup, wherein their outer free ends interact with the pad carrier plate of the brake pads. This yields a compact and effective construction.
In one embodiment, the retaining arms of the retaining stirrup may have elongated holes at fastening points to the retaining bow. This yields the advantage that centering and alignment relative to the brake disc center is easily possible by means of the elongated holes. The actual assembly and setting process is performed for the first time by the customer. Here, as a result of an application process, the air gap between disc and pads is set to 0 mm, and the spring assembly is braced between the pads. By means of the elongated hole in the retaining stirrup, the spring assembly can perform a centering movement, and is thus aligned exactly relative to the disc center. The elongated hole connection is subsequently fixed, and the air gap is set again.
In a further refinement, each spring arm may be formed, at the end, with a thrust section which, in its longitudinal direction, is formed with an elongated hole which is a guide section of the spring arm of the spreading device. In this way, a further relative movement capability can be achieved.
Furthermore, here, each thrust section may lie in each case on a bearing surface of a respective pad carrier plate, wherein the elongated holes of each thrust section interact in each case with a projection of the pad rear plate. This yields advantageous guidance in a radial direction.
The spreading device comprises two spreading elements, wherein a first spreading element acts on a first pad and a second spreading element acts on a second pad. The two spreading elements are connected to one another in the center (in relation to the carrier horns). It is thus possible to ensure a spring force which is identical—in a small tolerance range—both on the run-in side and on the run-out side. Different spring forces between run-out side and run-in side, which can lead to oblique wear, are minimized by way of the unilateral engagement of in each case one spring per pad.
A uniform application of force by the springs on the action side and on the reaction side, or on the thrust-piece side and on the caliper side, can be realized by way of a flexible adjustment of the center web. Furthermore, it is possible for slight incorrect geometrical positioning of disc, pad and carrier to be compensated by way of the flexible center web.
By way of the center web, it is possible for the active resetting device to be easily positioned and held down by the pad retaining stirrup. It is advantageously possible, during a pad change, for the resetting device to be easily removed and also exchanged.
Through the utilization of the entire pad slot between the carrier horns, it is possible for use to be made of spreading elements or springs with a very low spring rate in order to impart relatively constant forces in the event of pad wear. Owing to the long spring travels, the spring elements can be tolerant with regard to spring forces. The spring travels lead to a constant spring rate with low tolerances.
In a preferred design variant, only two springs are used.
The spreading elements may be formed from inexpensive and geometrically flexible metal sheets.
As a result of the offset with different centers of rotation, it is possible to replicate a relatively low spring rate. There is advantageously no need for a large number of windings (expensive, bulky).
Further advantages are:
Adjustability (of the centering)
Spring constants adaptable for each pad side, hence different for inside/outside and better adaptable to surroundings—within limits
Installation by way of center centering stirrup—compensates uneven force build-up
Possible “active” caliper centering
Active pad suspension by way of “fork” on the end of the spider
A further embodiment provides that the spreading device has at least one additional resetting element which, in addition to the engagement point/the engagement points of the spring arms, engages at a further engagement point on the respective pad carrier plate of a brake pad. This is advantageous because, in this way, an assisted resetting of the brake pads can be effected. A residual rubbing torque can thereby be prevented.
The at least one resetting element may, in one embodiment, be fastened by means of the retaining stirrup to the retaining bow. This yields a compact construction and a time saving during the installation process.
Alternatively, the at least one additional resetting element may be attached to a pad retaining stirrup, onto which it may be merely pushed, plugged or clipped. This yields a simple assembly process.
In one embodiment, the at least one resetting element is arranged with an upper retaining end in an opening of the pad retaining stirrup on an application-side wall of the opening, and makes contact, by way of a lower thrust section, with a thrust side of the pad carrier plate of a rear-side brake pad. This yields a compact and space-saving construction.
It is also possible for the at least one resetting element to have a spring arm, the upper end of which is attached via a spring coil with a fastening section to an application-side retaining end of the pad retaining stirrup, and a lower end of the spring arm, which is connected via a further spring coil with a clamping end, wherein the clamping end engages with a retaining section on the thrust side of the pad carrier plate of the application-side brake pad. A simple adaptation to resetting travels is thereby possible.
Here, the spring coils are formed as spiral springs with parallel longitudinal axes which run tangentially with respect to the brake disc, whereby a compact construction is made possible.
In another embodiment, the at least one resetting element may be attached to an application-side retaining end of the pad retaining stirrup and have a spring arm which is connected to a spring unit which in turn engages with a retaining section on the thrust side of the pad carrier plate of the application-side brake pad. An adaptation to greater resetting travels can also be easily achieved in this way.
It may alternatively be provided that the at least one resetting element is a spring unit which is attached to a base plate of an application section and which engages with a retaining section on the thrust side of the pad carrier plate of the application-side brake pad, whereby greater resetting travels can be achieved.
The spring unit may be formed as an evolute spring.
In a further embodiment, the at least one resetting element is formed from at least two spring units, of which both spring units engage, by way of in each case one spring end, with a retaining section on the thrust side of the pad carrier plate of the application-side brake pad, and wherein the at least two spring units are arranged in a plane.
Alternatively, the other spring ends of the at least two spring units may be in each case attached to a base plate of an application section of the brake caliper.
It is also possible for the other spring end of one spring unit of the at least two spring units to be attached to a pad retaining stirrup, wherein the other spring end of the other spring unit of the at least two spring units is attached to a base plate of an application section of the brake caliper. These above solutions with two springs yield the advantage that large resetting travels are possible in a small structural space.
A yet further embodiment provides that the at least one resetting element is at least one tension spring which is received in a bore in the application section of the brake caliper and which is fixed with one spring end in the bore, wherein the other spring end engages with a retaining section on the thrust side of the pad carrier plate of an application-side brake pad. Here, existing bores for fastening screws of the base plate may be used, whereby a compact construction is made possible.
In a yet further embodiment, it is advantageously possible for long resetting travels to be overcome by means of a self-adjusting resetting element. Here, it is provided that the at least one resetting element attached to the pad retaining stirrup is provided as a self-adjusting resetting element with a detent device which interacts with a detent section of the pad retaining stirrup.
Another embodiment provides that the at least one resetting element attached to the pad retaining stirrup is attached at both sides, by way of in each case one clamping end, to a rear-side retaining end of the pad retaining stirrup, wherein the clamping ends are connected in each case to a spring arm extending tangentially with respect to the brake disc, the other respective end of which spring arm, in the region of the sides of the pad carrier plate, is bent downwardly through 90° and is formed as a vertical spring arm and engages in each case by way of an outwardly bent spring end in each case with a lateral retaining section on the thrust side of a pad carrier plate of a rear-side brake pad. This construction, in the case of the spring elements being in wire form, is compact and simple.
If the at least one fastening section of the retaining bow is equipped with a fold section which makes contact with a collar of a corrugated bellows of a guide beam of the brake caliper such that the collar is fixed in a groove of the guide beam of the brake caliper, a conventional securing ring can be omitted, whereby a number of parts is reduced.
In one embodiment of the brake pad set, it is provided that a connection for a resetting element to the pad carrier plate of a brake pad has a retaining plate with an eyelet, wherein the retaining plate is arranged between a friction pad and a pad side of the pad carrier plate, and wherein the eyelet extends through a passage opening through the pad carrier plate and protrudes from a thrust side of the pad carrier plate. This is a simple alternative to production of the pad carrier plate by casting with cores and possible finish machining, whereby the costs required for this purpose can be omitted.
One embodiment of the brake pads provides that in each case elongate one intermediate space is arranged between a friction pad and a pad side of the respective pad carrier plate, whereby simple contacting for the spring arms of further resetting elements is realized.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
The expressions “top”, “bottom”, “left”, “right” relate to the respective arrangements in the figures.
A “top side” and a “bottom side” of a brake pad 3, 3′ or of a pad carrier plate 4 always relate to the installation situation of the respective brake pad 3, 3′. Here, the bottom side of the respective brake pad 3, 3′ is situated closer in a radial direction to a brake disc axis of rotation 2a than the top side of said brake pad 3, 3′, as can be clearly seen for example from FIG. 1.